Battery question 2008 Carrera

[tim997]

I left my key in the ignition for 48 hours. I also left a cell phone charger in the 12 volt outlet (not connected to the phone). Battery was dead. Using a basic battery tester I was able to determine that it was still putting our 3 to 6 volts. I attached the battery charger to the proper terminals, and triple checked for correct for polarity. When I plugged the charger in (set at 2 amps) the % charged needle on the Exide charger instantly deflected to full negative as if the polarity was reversed! I instantly disconnected the power and rechecked the terminal post connections which were correct. I have used this charger many times on other vehicles and have never seen this happen. I was afraid to purposely reverse the polarity at the terminal posts even though the charger has protection and will not operate in that configuration. I have fallen back to the CTEK charger through the 12 volt outlet in the passenger foot well and it is giving normal charging indications. I checked the Exide charger on another battery and the meter behaved normally. Appreciate any ideas about what is going on here. A Porsche grounding issue? Is the charger meter a voltmeter or an ammeter? For now I will leave the CTEK operating and check the battery voltage in the morning.

A related question: the battery is 6 years old and an original Porsche part from a dealer. Is there any problem with using other battery brands?

Many thanks,
Tim

[JayG]

PepBoys often has really good deals on Bosch batteries. Look for coupons on the website

[Steve Grosekemper]

Its a 2008 Carrera; show it a little love...
Just put in a new battery; Porsche factory or Interstate.
These cars have very sophisticated electrical systems.
After you get the new battery installed you will need to have the battery registered to the car.
Dealer or independent with PEWIS can take care of this.

[tim997]

I installed a drop in replacement from Interstate. No fault codes or warning lights. No radio code required. Thank you for the replies.

Tim